In many cases, injection substances must be brought together and thoroughly mixed before they are used, or specific solutions are to be formed. Examples are aqueous solutions, aqueous suspensions, O/W, W/O emulsions, solutions with soluble dry substances, oily solutions, oily suspensions, solutions with macrocrystals and compresses. Injection substances of the above type are brought together and mixed or dissolved immediately before they are used. In the simplest case, this is performed by placing the substances to be mixed in a small vessel and mixing or dissolving them, e.g., by shaking, whereby the thoroughly mixed injection substance may be drawn up into an injection syringe. This combination of an external vessel for the mixing of the injection substance and an injection syringe is also called a vial syringe. It is clear that, when injection substances of the above type are mixed and drawn up employing a combination of an external vessel and an injection syringe, high losses of one or more active ingredients may occur, as the injection substance placed in the vessel can never be completely taken up into the injection syringe. Moreover, the mixing and drawing up of an injection substance with the vial syringe requires some manual skills on the part of doctors and medical personnel.
Another system for the mixing and application of injection substances of the type mentioned consists of two normal injection syringes whose cannulae or cannula attachments are connected to each other by an attachable line. With this two-syringe system, the filled syringes are connected to each other by means of a connector and the plungers of the two syringes are operated in opposite directions, so that the substances are pumped to and fro between the two syringes. The reduction in cross-section which is caused by the cannula attachments or by the connection line in the connector compared with the syringe cylinders has a substantial throttling effect during the pumping process, the result of which is major turbulences in the flow and thereby a thorough mixing of the substances. However, it is also a drawback with this system that losses of an active ingredient always occur, as injection substance is always left in the syringe which is not used for the application and in the connecting line. In the case of expensive active ingredients, the losses caused thereby are substantial.
The so-called double-chamber syringe, in which the substances to be mixed are contained from the outset in two chambers of the syringe, functions in a similar way. The double-chamber syringe, like a single syringe, contains a plunger with a stopper at the end and also a second stopper which lies between the first stopper and the cannula attachment in the injection volume and divides the latter into a first chamber (between the cannula attachment and the second stopper) and a second chamber (between the first and second stoppers). When the plunger is pressed down, the second stopper is also moved hydraulically, as it were, via the first stopper by the suspension agent present in the second chamber, until it reaches a zone of the syringe cylinder in which the latter has a wider section (bypass) through which the suspension agent passes around the second stopper and overflows out of the first chamber into the second chamber. The substances thus brought together in the first chamber are then mixed by being shaken and the solution or suspension is thereby produced. However, the thorough mixing by means of shaking is not very effective.
An injection syringe with several chambers lying one behind the other in a cylinder for the administration of various injection agents is known from German Patent DE 730 362. The syringe has a syringe cylinder, a first plunger displaceable therein, which lies at its distal end with a stopper tight against the inner surface of the cylinder, and a displaceable second plunger which is guided and displaceable in longitudinal direction through the first plunger and which is fitted at its distal end with a second stopper, so that a first chamber is formed between the first and second stoppers and a second chamber is formed between the second stopper and the bottom of the syringe cylinder which carries the cannula, the two chambers being completely separated from each other by the second stopper. The syringe is also fitted with a bypass line which connects openings in the side wall of the syringe cylinder to the cannula line. The syringe serves to inject an injection agent and, separate therefrom before or after the injection agent, another agent, for example an indifferent solution. In use, the injection agent is drawn up into the first chamber and the solution into the second chamber, with the second stopper being so positioned that it blocks the openings in the cylinder wall to the bypass line. Solution can then be injected first by pressing down the second stopper with the second plunger. As soon as the second stopper has been pushed down a certain distance, it frees the openings in the cylinder wall, as a result of which a link from the first chamber to the cannula is produced through the bypass line. The injection agent can then be injected from the first chamber with the first plunger by pressing down the first stopper with the first plunger. A thorough mixing of the agents in the first and second chambers is not possible with this syringe arrangement.
In EP 0 511 183 A1 there is disclosed a double-chamber syringe with a first chamber with a solvent or suspension agent and a second chamber which contains the substance to be dissolved or suspended. A first stopper, displaceable with a plunger, is arranged in the first chamber and a second displaceable stopper, which separates the two chambers from each other, is arranged in the second chamber. The second displaceable stopper contains a valve element which is raised from its seat by hydrostatic pressure, which is created by advancing the first stopper, and opens a throughflow path from the first into the second chamber. The solvent/suspension agent can be completely forced into the first chamber by advancing the first stopper. There, mixing takes place simply by the uniting of the two agents. The actual injection is carried out when the second stopper is advanced by pressure with the first plunger, in order to thereby drain the first chamber through a cannula. The known double-chamber syringe provides no measures which would make possible an active thorough mixing of the substances which are united in the first chamber.